Voltage reference circuit



United States Patent 3,310,731 VOLTAGE REFERENCE CIRCUIT Arthur Ostrotl,Woodland Hills, Calif., and Michael DAgostino, Philadelphia, Pa.,assignors to Radio Corporation of America, a corporation of DelawareFiled Jan. 29, 1963, Ser. No. 254,772 6 Claims. (Cl. 3234) Thisinvention relates to voltage reference circuits which function tomaintain the output voltage of the circuit equal to the input voltage ofthe circuit.

A volt-age reference circuit provides an output voltage which issubstantially identical to some input reference voltage level andthec'ircuit tracks variations in the input reference voltage level tokeep the output voltage substantially identical thereto. A voltagereference circuit may, for example, be utilized with a ferrite corememory which is subject to temperature changes. Although the voltagereference circuits illustrate-d herein are for such use, it may be usedin other ways, as well.

In ferrite core memories, temperature changes tend to change thehysteresis loop characteristic of the ferrite cores in a manner whichmay cause erroneous switching of the ferrite cores when only half-selectdrive currents are applied to the cores. To prevent such errors, atemperature sensitive device, such as a thermistor, is mounted in thememory and connected in a manner to provide the input reference voltagelevel for the voltage reference circuit. The output of the voltagereference circuit faithfully tracks voltage changes in the thermistornetwork. This output voltage is applied to controlled circuits to varythe half-select memory drive currents in a manner to compensate for thetemperature changes in the memory.

Since the drive currents vary appreciably in magnitude, dependent on thedata being processed in the memory, the temperature variations therein,and because of the manner in which the reference voltage is applied tothe controlled circuits, the voltage reference circuit should alsofunction as a current sink circuit to absorb excess current applied tothe output voltage terminal thereof.

Furthermore, the current variations should be absorbed by the voltagereference circuit without causing a change in the output voltagethereof.

Accordingly, it is an object of this invention to provide a new and animproved voltage reference circuit.

It is another object of this invention to provide a new and improvedvoltage reference circuit which functions as an efiicient current sinkcircuit.

A voltage reference circuit embodying the invention includes first andsecond transistors of opposite conductivity type but complementary toeach other. A reference voltage source is coupled between the base andcollector electrodes of said first transistor while the emitterelectrode thereof is coupled to the base electrode of said secondtransistor.

A load is connected to the emitter of the second transistor so that thefirst and second transistors operate as a pair of cascaded emitterfollower stages. The output voltage derived from across the load, andapplied to the controlled circuits, is substantially equal to thevoltage level of the reference voltage source and also track's voltagevariations in the reference voltage source because of the emitterfollower operation of the first and second transistors.

The voltage reference circuit functions as an eflicient current sinkcircuit by utilizing a third load transistor of the same conductivitytype as the second transistor as the load on the second transistor andby providing a feedback path between the load and second transistors.The emitter-*to-collector current paths of the second and loadtransistors are serially connected together and the feed- 3,319,731Patented Mar. 21, 1967 back path is provided by coupling the collectorelectrode of the second transistor to the base electrode of the loadtransistor. By these connections, the output voltage developed acrossthe load transistor remains substantially the same as the input voltageeven though appreciable variations occur in the current applied to theload transistor by the controlled circuits.

The novel features which are considered to be characteristic of thisinvention are set forth with particularity in the appended claims. Theinvention itself, however, 'both as to its organization and method ofoperation as Well as to additional objects and advantages thereof, willbest be understood from the following description when read inconjunction with the accompanying drawing, in which:

FIGURE 1 is a schematic circuit diagramof a voltage reference circuitembodying the invention; and

FIGURE 2 is a schematic circuit diagram of a portion of anotherembodiment of the invention.

Referring now to FIGURE 1, a voltage reference circuit 10 embodying theinvention includes a pair of transistors 11 and 12 of oppositeconductivity type but complementary to each other. The transistors 11and 12 comprise a pair of the emitter follower stages, coupled incascade, to produce an output voltage which is substantially identicalto the voltage exhibited by a reference voltage source 13. The firsttransistor 11, which is, for example, of the PNP conductivity type,includes base 14, emitter 15, and collector 16 electrodes. The referencevoltage source 13, which is illustrated as being variable, is connectedbetween the input base electrode 14 of the transistor 11 and a point ofreference potential, or ground, in the circuit 10. The collectorelectrode 16 is connected directly to ground and thus the source 13 isconnected directly across the base 14 and collector 16 electrodes of thetransistor 11. The emitter electrode 15 of the transistor 11 is coupledthrough a load resistor 20 to a positive terminal 22 of a source ofenergizing potential, V By these connections, the transistor 11 isbiased for linear operation in a common collector, or emitter follower,configuration.

The second transistor 12, which is of the NPN conductivity type andcomplementary to the first transistor 11 includes base 26, emitter 28and collector 30 electrodes. The output emitter electrode 15 of thetransistor 11 is coupled directly to the input base electrode 26 of thetransistor 12. The collector electrode 30 of the transistor 12 iscoupled through a resistor 32 to the positive potential terminal 22 ofthe source of energizing potential, V The emitter electrode 28 of thetransistor 12 is coupled to a load transistor 34, which is a part of theload on the second emitter follower transistor 12.

The load transistor 34, which is of the NPN conductivity type, includesemitter 36, base 38, and collector 40 electrodes. The collectorelectrode 40 of the load transistor 34 is directly connected to theemitter electrode 28 of the second transistor 12. The emitter electrode36 of the load transistor 34 is grounded. Thus, the emitterto-collectorcurrent paths of the second and load transistors 12 and 34 are seriallyconnected together with the second transistor 12 operating as an emitterfollower and the load transistor 34 functioning as the load thereon. Aterminal 42 at the collector electrode 40 of the load tran sistor 34provides an output terminal for the circuit 10. The output voltagedeveloped from the terminal 42 to ground, or across the load transistor34, is applied to control the controlled circuits 43. The base electrode38 of 0 the transistor 34 is coupled through a resistor 44 to the to thenegative potential terminal 46. The Zener diode,

in its reverse breakdown condition, maintains a substantially constantvoltage difference between the collector electrode 30 of the transistor12 and the base electrode 38 of the transistor 34. It is, of course,apparent that other coupling devices, such as a parallelresistor-capacitor combination could be utilized instead of the Zenerdiode 50, but the Zener diode t) exhibits a greater sensitivity in thefeedback path.

The voltage sources V and V may, for example, comprise a single,grounded, center-tapped power supply with the terminal 22 being theabove-ground positive terminal thereof and the terminal 46 being thebelow-ground negative terminal thereof.

In operation, the output voltage appearing at the output terminal 42 ofthe voltage reference circuit will be substantially equal to the voltageexhibited by the reference voltage source 13. Furthermore, the outputvoltage of the circuit 10 will closely follow in both direction andmagnitude any variations in the voltage level exhibited by the referencevoltage source 13. The emitter voltage of the first transistor 11 isequal to the voltage level of the reference voltage source 13 plus thesmall junction voltage of its forward biased emitter-base junction. Thevoltage appearing across the load transistor 34, or the emitter voltageof the transistor 12, is equal to the emitter voltage of the transistor11 minus the small junction voltage across the forward biasedemitter-base junction of the transistor 12. Since the transistors 11 and12 are selected to be complementary, the emitter-base junction voltageof the transistor 11 is substantially equal and opposite to theemitter-base junction voltage of the second transistor 12, so theycancel each other. Thus, in quiescent operation, the output voltage ofthe voltage reference circuit 10 is identical to the voltage of thesource 13.

If the reference voltage level from the source 13 changes, the emittervoltage of the transistor 11 changes in the same direction andsubstantially the same amount. This change in voltage is coupleddirectly to the base eleo trode 26 of the transistor 12 and causes theemitter voltage of the transistor 12 to similarly change in the samedirection and substantially the same amount. Thus, the cascaded emitterfollower transistors 11 and 12 produce an out-put voltage which issubstantially identical to the reference voltage of the source 13regardless of voltage variations in the source 13.

The second emitter follower transistor 12 and the load transistor 34also function as an eflicient current sink by absorbing varyingcurrent-s applied to the output terminal 42 from the controlled circuits43, and without causing the output voltage to vary from the referencelevel exhibited by the source 13. If the current input to the terminal42 of the circuit 10 increases, the voltage from the output terminal 42to ground, or across the load transis-tor 34, also tends to increase.The increase in positive voltage at the collector of the load transistor34 tends to decrease the forward bias across the emitterbase junction ofthe NPN transistor 12 and reduces the current flowing through thistransistor. The decreased current flow through transistor 12 tends toincrease the current flow through Zener diode 50. The increased currentthrough Zener diode is applied to the base electrode 38 of the loadtransistor 34. The increased base current of load transistor 34 causesthe emitter base junction of the load transistor 34 to become moreforwardly biased, causing an increased current fiow through thetransistor 34 and a decreased impedance to be exhibited by thistransistor. The output volt-age is therefore r 4. turned substantiallyto its initial value and the load transistor 34 absorbs the increasedcurrent input from the controlled circuits 43. An opposite sequenceoccurs, if the input current decreases.

The current from the energizing potential sources V and V remainssubstantially at its quiescent level. However, in the example described,a greater current flows through the Zener diode 50 and a reduced currentflows through the emitter follower transistor 12. The sum of these twocurrents remiains substantially constant in the quiescent, transient,and steady state conditions of operation. Thus, the voltage referencecircuit 10 functions as an efficient current sink while maintaining theoutput voltage at a particular reference level, regardless ofsignificant changes in the input current.

With large current increases from the controlled circuit 43, the loadtransistor 34 of FIGURE 1 may tend to overload. In FIGURE 2 is shown apartial schematic circuit diagram of another embodiment of the inventionadapted for longer current operation. In this embodiment of theinvention a second load transistor 60 is cascaded in an emitter followerconfiguration with the first load transistor 34 to provide increasedcurrent gain to absorb larger input currents to the terminal 42. Thesecond load transistor 60 includes a base electrode 62 which is coupledto the terminal 48 of the voltage reference circuit 10 of FIGURE 1, acollector electrode 64 which is directly coupled to the output terminal42 of the circuit 10, and an emitter electrode 66 which is directlycoupled to the base electrode 33 of the first load transistor 34. Theembodiment of the invention shown in FIG- URE 2 operates in a similarmanner to the embodiment of FIGURE 1 but due to an increased feedback,increased current gain enhances the current absorbing capability of thevoltage reference circuit 10, without causing changes in the outputvoltage thereof. Additional stages of load transistors may be coupled tothe load transistor 34, in the same manner as the load transistor 60, tohandle larger currents from the controlled circuit 43.

It is to be noted that the embodiments of the invention disclosed inFIGURES 1 and 2 may be operated at a low current level from the sourcesV and V in the quiescent state. In the quiescent state, the voltagereference circuit 10 draws only enough current to place the emitterfollower transistor 12 in a desirable region of operation. Furthermore,the current remains substantially constant during transient and steadystate operating conditions, merely dividing differently through theZener diode 59 and emitter follower transistor 12. An increase incurrent in one of these components is balanced by a substantiallyequivalent decrease in current in the other. Therefore, the circuit 10exhibits a low level power consumption from the power supply V and V andthe power supply need not be a high level power supply nor need it bewell regulated. Thus, there is a considerable advantage over other knownvoltage reference circuits. Furthermore, should the circuit 10 berequired to handle large current inputs from the controlled circuit 43,no change in the power supply is necessary. Additional load transistorsmay be added in tandem to the load transistors 34 and 60 to absorb thelarger current.

A voltage reference circuit 10, modified as illustrated in FIGURE 2, wasconstructed using the values and type of components shown in FIGURES 1and 2. This circuit accommodated peak currents of 250 milliamperes withless than a 1% variation in output voltage.

What is claimed is: 1. An electrical circuit comprising in combination:a pair of transistors of the same conductivity type with each havingbase, emitter, and collector electrodes,

means for serially connecting together the emitter-tocollector currentpaths of said transistors so that one transistor functions as an emitterfollower and the other functions as a load thereon,

biasing means for forward biasing the base electrode of each of saidemitter follower and load transistors with respect to the emitterelectrodes thereof, and

means for transmitting potential changes on said collector electrode ofsaid emitter follower transistor to the base electrode of said loadtransistor including a direct current conductive device connectedbetween said collector and base electrodes of said emitter follower andload transistors, respectively.

2. An electrical circuit in accordance with claim 1,

wherein said direct current conductive device comprises a Zener diode.

3. An electrical circuit comprising in combination:

a pair of transistors of the same conductivity type with each havingbase, emitter, and collector electrodes,

means for serially connecting together the emitter-tocollector currentpaths of said transistors so that one transistor functions as an emitterfollower and the other functions as a load thereon,

a source of energizing potential having opposite polarity terminals,

first and second resistors coupled from the collector and baseelectrodes, respectively, of said emitter follower transistor to oneterminal of saidsource of energizing potential,

a third resistor coupled from the base electrode of said load transistorto the other terminal of said source of energizing potential,

means including said source of energizing potential for forward biasingthe base electrodes of said pair of transistors with respect to theemitter electrodes thereof, and

means for transmitting potential changes on said collector electrode ofsaid emitter follower transistor to said base electrode of said loadtransistor including a Zener diode coupled from the collector electrodeof said emitter follower transistor to the base electrode of said loadtransistor,

said Zener diode being poled to conduct in a reverse direction from saidcollector to said base electrode to maintain a substantially constantvoltage ditfer ence therebetween,

whereby current input variations to the collector electrode of said loadtransistor which tend to cause the collector voltage of said loadtransistor to vary cause current and voltage variations at the collectorelectrode of said emitter follower transistor which variations arecoupled through said Zener diode to vary the base current of said loadtransistor in a direction to maintain the voltage at the collectorelectrode thereof substantially constant.

4. A voltage reference-current sink circuit comprising in combination:

first and second transistors with each having base, emitter, andcollector electrodes,

means connecting said first and second transistors in a cascaded emitterfollower configuration,

a voltage reference potential source coupled between the base andcollector electrodes of said first transistor,

a load transistor having base, emitter, and collector electrodes,

means coupling said load transistor to said second transistor so thatthe emitter-to-collector current paths of said second and loadtransistors are serially connected, and

means providing a direct current conductive connection between thecollector electrode of said second transistor and the base electrode ofsaid load transistor.

5. A voltage reference-current sink circuit in accordance with claim 6,wherein said direct current conductive connection comprises a Zenerdiode poled to conduct in a reverse direction from said collectorelectrode of said second transistor to the base electrode of said loadtransistor.

6. A voltage reference-current sink circuit comprising in combination:

first and second transistors of opposite conductivity type with eachhaving base, emitter, and collector electrodes,

means coupling the collector electrode of said first transistor to apoint of reference potential in said circuit,

a reference voltage source coupled between the base electrode of saidfirst transistor and said point of reference potential,

a source of energizing potential having opposite polarity terminals,

a resistor coupled from the emitter electrode of said first transistorto one terminal of said energizing source,

means coupling the base electrode of said second tran sistor to theemitter electrode of said first transistor,

a resistor coupled from the collector electrode of said secondtransistor to said one terminal of said energiZing source,

a load transistor having base, emitter, and collector electrodes,

means coupling the emitter electrode'of said load transistor to saidpoint of reference potential,

means coupling the collector electrode of said load transistor to theemitter electrode of said second transistor so that said load transistorfunctions, as a load on said second transistor,

a resistor coupled from the base of said load transistor to the otherterminal of said energizing source, and

a Zener diode coupled from the collector electrode of said secondtransistor to the base electrode of said load transistor,

said Zener diode being poled to conduct in a reverse direction in abreakdown condition thereof from the collector electrode of said secondtransistor to the base electrode of said other transistor.

References Cited by the Examiner UNITED STATES PATENTS 3,124,698 3/1964Semmer 30751 3,174,095 3/1965 Cocker 32322 3,241,045 3/1966 Brosseau32322 3,243,690 3/1966 Gately 32322 OTHER REFERENCES Hunter, L. P.:Handbook of Semiconductor Electronics, McGraw-Hill Book Co., Inc., N.Y.,1962, pp. 17-18.

JOHN F. COUCH, Primary Examiner.

K. D. MOORE, Assistant Examiner.

3. AN ELECTRICAL CIRCUIT COMPRISING IN COMBINATION: A PAIR OFTRANSISTORS OF THE SAME CONDUCTIVITY TYPE WITH EACH HAVING BASE,EMITTER, AND COLLECTOR ELECTRODES, MEANS FOR SERIALLY CONNECTINGTOGETHER THE EMITTER-TOCOLLECTOR CURRENT PATHS OF SAID TRANSISTORS SOTHAT ONE TRANSISTOR FUNCTIONS AS AN EMITTER FOLLOWER AND THE OTHERFUNCTIONS AS A LOAD THEREON, A SOURCE OF ENERGIZING POTENTIAL HAVINGOPPOSITE POLARITY TERMINALS, FIRST AND SECOND RESISTORS COUPLED FROM THECOLLECTOR AND BASE ELECTRODES, RESPECTIVELY, OF SAID EMITTER FOLLOWERTRANSISTOR TO ONE TERMINAL OF SAID SOURCE OF ENERGIZING POTENTIAL, ATHIRD RESISTOR COUPLED FROM THE BASE ELECTRODE OF SAID LOAD TRANSISTORTO THE OTHER TERMINAL OF SAID SOURCE OF ENERGIZING POTENTIAL, MEANSINCLUDING SAID SOURCE OF ENERGIZING POTENTIAL FOR FORWARD BIASING THEBASE ELECTRODES OF SAID PAIR OF TRANSISTORS WITH RESPECT TO THE EMITTERELECTRODES THEREOF, AND